Production of castings free from pipes and blow-holes



W. ROHN June 30, 1931.

PRODUCTION OF CASTINGS FREE FROM PIPES AND BLOW HOLES Filed Sept. 16,1927 aoooodoooo v//////////////////n1 .rlfll/w -1:

Inventor: W

o oooooooo Patented June 30, 1931 1 W'ILHEIJM BORN, OFHANAU-ON-THE-MAIN, GERMANY PRODUCTIQN OF CASTIIIGS FIE-3E FBOIVI PIPESAND BLOW-HOLES Application filed September 16, 192., Serial No. 220,054,and in Germany December 28, 1925.

Blocks, sheets and articles of other shapes were hitherto produced insuch a manner that the molten smelt from the furnace or the crucible wascast into a suitably selected mould and allowed to solidify therein. In.this method there is always observed the disadvantage t-hat the castarticles which are 'ol t-ained,.in spite of the casting methods whichhave been modified a considerable numit her of times, are never obtainedfree from pipes and blow-holes. so that a considerable waste occurs byreason of the lost head. There will now he described a method ofproducing such articles in a convenient. manner and free from pipes andblow-holes.

The fundamental idea of the. invention is not to pour the. molten metalinto a separate mould. but to allow it'to solidify in the crucibleitself. and to so select the cooling conditions that no pipes orblow-holes can be formed. On the same principle is also based forexample, the production of the single crystals of salt and metal smeltsbutthe y use of such a. method of operation for the production of blocksfree from pipes and blowholes wasnot known hitherto. The problem underconsideration can be solved by causing the smeltto solidify from thebottom upwards. This can be effected by mounting the f t crucible on avertically movable support.

After the termination of the smelting process this sup iort is lowered,and the crucible is fthlls brought with the bottom firstgradually intocolder'zones, in such a manner that the bottom. of the crucible firstcomes into the lower temperature, and the cooling of the crucibleproceeds from the bottom upwards.

In order to enable the cooling to be better I controlled it ispreferable to provide in the lower part-of the furnace, or under thebottom thereof stationary copper tubes, which pass round the support incircles and through which cooling water flows.

The-same result can be obtained for example in anelectrically heatedfurnace by subvidmg the heat-ingkcoil. and after the com- ..pletion ofthe fusion cutting this outin sections. beginning at the bottom atsuitably h selected periods of time. Ir an inductively heated electricsmelting lurnace the same resultcan be obtained by switching off thewindings of the induction coil gradually. separately. or in groups, fromthe bottom, until finally the whole coil has been cut out. The actioncan also be supported or controlled by increasing the thickness of layerfrom the bottom upwards, of the refractory material between the smeltand the oven coil, which, for example. is water-cooled. In order toprevent a too early freezing of the upper layers of the smelt. there ispreferably suppliul to the upper coils. which still remain in operation.somewhat more energy than is actually required by them for participatingin the complete-operation of the furnace. Finally, such control may alsobe obtained by slowly raising the complete induction coil or the furnacecasing.

A constructional example for an induction furnace, free from iron. isillustrated in Figs. 1- tofl. In these. (1 indicates the crucible whichis mounted on the support 7). which is passed through an opening I inthe bottom of the furnace. and for example can be. moved vertically bytoothed wheel gear I]. so that "after the completion of the smelting thesupport-.7). together with the crucible a can gradually'be lowered fromthe top downwardly. f indicates the. windings of the primary coil.Underneath this may be provided a cooling device in the form of copperpipes through which watercirculated. In the form of constructionaccording to Fig. 2 the primary coil. after completion of the smelting.is raised at a suitably selected speed by a suitable device. for exampleby weights guided over rollers. According to Fig. 3 the coil f isprovided with tapping points g. (I, which enable sections of the coil tobe cut out in stages. In the example of the circuit illustrated in thedrawing the two lowermost windings are disconnected by moving the switchh from the segment 1 to the segment 2, on movement to segment 3 the nexttwo windings and so forth. The production of the desired action may, ifnecessary. also be promoted by allowing a sufiiciently thick plate ofrefractory and heating insulating material to float on the surface ofthe smelt or by placing simply on the surface of the smelt a layer ofgranular, refractory material. A suffciontly thick layer of slag ofsuitable composition may also act in this respect.

For this method of operation. the smelting vessel. particularly when ahigh-frequtaicy furnace is used as the smelting furnace. may

he of any suitable. shape. so that it. is possible to obtain mouldedarticles of any suitable character. The heating winding or primary coili:-= preferably arranged to snit the moulded article to lo produced. Inthis manner it is possible to obtain with -full certainty mouldedcastings free from blow-holes. A |ulrti ularly suitable application isthe direct l'u'odu tion ol' slab blooms free from blowhol s. whichdirectly hate the most suitable shape for rolling plates.

It may be mentioned that a very advantageous method of operation isobtained when the above method is combined with the preparing methodaccording to British specification Xo. 2:26.801. For this purpose itisadvisable to adapt the method of operation according to Britishspecification No. 22(530]. in the manner illustrated in Fig. 4 inaccordance with the requiiementsof the new method ofoperation. Forexample. in induction furnaces. free from iron. the lower opening of thesomewhat cylindrical induction coil 1' is closed by a chamotte plate Zr.7. formed of one or more parts. Onto this chamotte plate. is firstlycharged up to a pre-determintal depth of the layer a granular or sandymaterial 7 such as ground bauxite which at the temperatures occurringduring the operation is not capable of sintcring. There is then placedinside the 'coil on this layer a thin railed sheet-metal cylinder spacebet ween the J11. and the intermediate sheet-metal cylinder in and theinthiction coil 5 is filled with the same granular or sandy materialwhich doesl'iot sinter at the temperatures which occur. Into theinterior of the sheet-metal cylinder there is then placed for example. asheet-metal cas .a ldition. if nos-iced, of powdered mg 'n. of which theouter shape t -orrespomls with the surface of the. casting to besubsequently produced. according to British Patent 226.801 and in theinterior of which is placed the :aterial to be fused. mediate spacebetween this sheet-metal templateyli and the sheet-metal cylinder in isfilled with a granular or sandy material such as ground magnesite. oralumina. with the glass or horic acid which at the temperaturesoccurring during the operation, is capable of sintering and retainingits shape. After the charging of the furnace ha been completed in themanner indicated, the sheet-metal cylinder in is withdrawn. whereby thetwo layers of non-sinteri|;g granular or sandy material 7. and thesinteringmaterial 0 are notintermixed. but simply put in contact withone another. This material 0. by reason of the fact that it sinters attemperatures The interthe fusion point of the alloyto be extent. ashapewhich are somewhat below of the metal to be fused. or fused, thusforms to some retaining crucible. In the upper opening of the inductioncoil ithe temperature under the circumstances will not be suilicientlyhigh in order to ell'ect u sutlicient sintering of the shape retainingmaterial 0. It may consequently be adrisable when setting up the furnaceto insert at. this pointa tubular section of refractory material as isindicated in the drawing of the. furnace at p. Iirorder to obtain asufficient increase in temperature in these upper zones it may beadvisable to cover the upper opening oi. the fusion chamber by a thickrefractory plate or to apply a layer of granular or sandy refra ct orymaterial.

During the fusion process the material Z will still be, capable ofcrumbling. as this mass is ot adapted to sinter at. the temperatureswhich occur during operation. The mass 0 however, will sinter togetherinto a. shape-retaining crucible of like body at; tempertures which are.below the temperature at which the. fusion commences. After thecompletion of the fusion the separate sections of the induction coil.commencing from the bottom. are disconnected in stages at suitable.intervals of time and thus the smeltis caused to solidify from thebottom upwards. free from bimv-holes and pipes. After the completion ofthe smelting and solidification the chamotte plate l' is partly orwholly drawn to one side and the. material 7. which is still capable ofcrumbling. is allowed to run out downwardly. As soon as this has beendone the casting which has been produced in the interior of theinduction coil. with its surrounding sintered layer a is freely exposed.v and can be I'(.'t (lll removed. either upwardlv or do\\'n\\':u'dl fromthe. induction coil. whereupon the furnace. can be recharged. The layer7. which has notsiut-ered and which has remained capable of crumbling,and is between the siutered part- 0 and the coil or the heating element.also serves as a. protection. against furnace breahages. Should a crackoccur in the sintered layer 0 for any reason. this could not becontinued through the layer 7 as this layer remains crumbly and wouldthus I'HCfttll the passage of metal to the coil. Finally it is advisablealso to combine the method of operation with that according to which theouter space between the coil or the heating element and the furnacecasing is filled with a crumbly. sandy mate rial. H in the cast! of anaccident. there should be such a collapse of the materials I and 0 that.the molten smelt should come in contact with the induction (:oil or theheatingelemcnt then the smelt could not. pass into the space outside theinduction coil or the heating element, and consequently could not;

zone adjacentthe iii Zii

come into contact with the furnace casing and thus damage this.

Finally it is possible to work a furnace oprated in accordance with theconstruction bove described readily in a gas-tight casing (see Fig. l)and to allow the fusion operation to take place in a protectingatmosphere or in a vacuum. As in accordance with the im'ention. theblock, free from pipes and blmv-holes. is produced at the place offusion without casting, itis not necessary to provide separate devicesfor carrying out the casting in a protecting atmosphere or a vacuum, orto arrange the furnace together with the easing so as to be capable ofbeing tilted for this urpose. This is of considerable importance in thecase of induction furnaces free from iron as in such uses, as is wellknown. the

casing must either consist of a non-comluctlag material (for example,earthenware) or of a 1ioor-comlucting metallicmaterial which in additionmust also be subdivided in a suitable manner so as to be electricallynon-conducting. lloth in the case of earthen "are casings and subdividedmetal casings the device for tilting causes considerable difliculties byreason of the mechanical strains to which the furnace is subjected, andit is therefore to be regarded as a technical improvement that the abovedescribed construction and methods of operation enable blocks 2 nd':i.-ting;-: free from pipes and blow-holes to be produced in aconstantlystationary furnace.

While 1 have shown and described my improved process and the-means forproducing castings free from blmv-holes and pipes as pointed out. above,I do not wish to limit my' self to the exact steps and nit-ans describedas I am aware that two or more of the steps described may be combinedand man minor changes may be made in them without dcpariing from thespirit of my inventi n. and I claim such equivalents as may suggestthemselves to those skilled in the art.

I claim:

1. The method of producing castings free from pipes and blow-holes insmelting furuaces, which consist in melting the metal in the furnace.particularly in electrically heated furnaces such as resistance furnacesor induction and high-frequency furnaces and gradually solidifying theentirely molten metal from the bottom upwards in the smelting vessel.

2. The method of producing castings free from pipes and blow-holes inelectrically heated smelting furnaces which consists in thoroughlymelting the material in the furnace and then successively eliminating atan adjustable speed the action of the heating device from the bottom ofthe smelting vessel upwards.

3. The method of producing castings of a determined shape free frompipes and blowholes such as slab blooms for rolling plates whichconsists in smelting the metal or the solidifying the thoroughlyliquefied metal from the bottom upwardly in the smelting vessel.

The method of producing ferrous metal castings free from pipes and blowholes in a ceramiclined smelt-lug furnace particularly in electricallyheated furnaces such as resistance furnaces or induction and highfrequency furnaces which consists in melting the metal in the furnace.and gradually solidify ing the entirely molten metal from the bottomupwardly in the smelting vessel.

(3. The method of producing castings free from pipes and blow-holes inelectrically heated smelting furnaces such as resistance or inductionand high-frequence furnaces which consists in first forming asheet-metal casing of which the outer shape corresponds with the surfaceof the casting to be produced, surrounding the said casing with a.

layer of a granular material capable of sintering closebelow the meltingtemperature of the material to. be smelted, surrounding the said layerwith a layer of a granular material not sintering at the saidtemperature, then introducing the metal to be smelted into the interiorof the metal casing, heating the 'metal by means of an electric currentup to the molten state and gradually solidifying the molten metal, aftercompleting the melt, from the bottom upwards in the smelting vessel.

7. The method of producing castings free from pipes and blow-holes inelectrically heated smelting furnaces such as resistance or inductionand high-frequency furnaces. which consists in first forming a sheetmetal casing of which the outer shape corresponds with the surface of"therasting to be produced, surrounding the said casing with a layer of agranular refractory material capable of sintering close below the meltintemperature of the material to be smelted:

surrounding the said layer with a further layer of a granular materialnot sintering at the temperature produced between the layer beingcapable of sintering and the heating devices. then introducing the metalto be smelted into the interior of the metal casing, heating the metalby means of an electric current up to the molten state, graduallysolidim: H m

fying the molten metal, after completing the melt, from the bottomupwards in the smelthe method of producing castings free from pipes andblow-holes in electrically heated smeltim furnaces such as resistance orinduction and 1gh-f equency furnaces which materinl capable of sintermgclose below the melting temperature of the material to be smcltwl, andan upper, smaller part with a. tube of refractory material, surroundingthe m layer of granular material, not sintering at I an electric currentup to molten state, and

I 25 gradually solidifying the molten metal, aftif; V er completing themelt, from the bottom upwards in the smelting vessel.

. gg, 9. The method of producing castings free 5x: from pipes andblow-holes in electrically as heated smelting furnaces such asresistance as duced, surrounding the said casing with a 49 granularmaterial. extending to the outer to e smeltedinto the interior of' themetal 4.; casing, heating the metal bv mean's of an wards in thesmelting vessel. 50 n testimony whereof I aflix my signature WILHELMROHN.

